The invention relates to a device and a method for removing moisture from a battery housing, and to a battery housing, a battery disconnect unit and a battery system. The invention additionally relates to a vehicle, in particular a motor vehicle such as an electric motor vehicle or hybrid vehicle, having the battery system.
It is foreseeable that, both in the case of stationary applications, for example in wind turbines, and in the case of mobile applications, for example in electric motor vehicles (electric vehicles, EV) or hybrid vehicles (hybrid electric vehicles, HEV), new battery systems, for example having lithium-ion accumulators or nickel-metal hydride accumulators, will increasingly be used as rechargeable batteries.
The battery systems must meet very demanding requirements in respect of the usable energy content, charging/discharging efficiency, reliability, service life and the unwanted loss of capacity resulting from frequent partial discharging (Memory Effect).
A battery system comprises a multiplicity of battery cells. Owing to their cell internal resistance and the occurring electrochemical processes, the battery cells heat up during charging and discharging. The battery cells may be connected in series, in order to increase the voltage, and/or in parallel, in order to increase the maximum electric current. The battery cells in this case may be combined to form battery units, or battery modules. When used for driving vehicles, approximately 100 battery cells, for example, may be connected in series or in parallel (as a traction battery). In the case of a high-voltage battery system, the total voltage may thus be, for example 450 V or even 600 V.
The allowable temperature range for the operation of the battery cells is typically between −30° C. and +70° C. In the lower range of the operating temperature, the performance of the battery cells may diminish significantly. Irreversible damage to the battery cells may also occur in this case. If the operating temperature is exceeded, also, the performance of the battery cells may diminish significantly. Likewise, irreversible damage to the battery cells may occur in this case. The damage may result in accelerated aging of the battery cells, or in thermal runaway of the battery cells, which represents a hazard to humans and the environment.
In order to ensure the safety and function of the battery system, it is therefore necessary to operate the battery cells within the prescribed temperature range. On the one hand, during the operation of the battery cells heat is produced, which must be removed in order to avoid heating of the battery cells above the critical maximum temperature. On the other hand, in the case of low temperatures, it may be necessary to heat up the battery cells to a minimum temperature. For the purpose of maintaining the prescribed temperature range, the battery system is tempered, i.e. cooled or heated as appropriate.
For this purpose, the battery system may comprise a fluid, for example a liquid such as alcohol, for example propane-1,2,3,-triol (glycerol, glycerin), oil or water, or a liquid mixture, as a tempering agent in a tempering agent circuit.
If a housing of the battery system is not hermetically sealed (gas-tight), moisture, for example in the form of water vapor, may continuously enter the battery system, for example through seals. Since, during cooling of the battery system, the tempering agent temperature is significantly below the temperature in the housing, condensate (condensation water, condensed water) may form. Consequently, water in liquid form, either pure or as a liquid mixture, may form and/or collect in the battery system. Liquid water, for example raindrops, mist droplets and solid water, for example ice and snow crystals, are not classed as air moisture.
Battery cells may be combined to form battery modules or battery packs. In the case of a battery pack, the battery cells may be disposed in a metallic frame structure, which is disposed in a wrapping of a flexible, watertight plastic film. In this case, the risk of the formation and collection of condensate water (condensation) is increased.
In order to ensure the safety of the battery system, in particular the high-voltage battery system, it may additionally be necessary to be able to break the electric circuit, for example by means of a switching means such as a relay, a contactor, in particular a power contactor, or a switch. The switching means must transmit large currents, for example several 100 A, and also be able to cut out safely. Protection against short-circuit currents may be effected, for example, by means of an overcurrent protective means such as a fuse, in particular a safety fuse. The switching means, the overcurrent protective means and/or a sensor means may be disposed, for example, in the battery system or a battery disconnect unit (BDU).
Owing to temperature differences and/or temperature changes, therefore, there is a risk of condensation water forming in the battery system or in the battery disconnect unit. Owing to the condensation water, there is a risk of damage and/or failure of the electrical and/or electronic components, for example the battery cells, the switching means, the overcurrent protective means and/or the sensor means, as a result of corrosion, and/or a jeopardizing of safety. In the case of an impact caused by an accident, for example, there may therefore be a high safety risk because of the battery system and/or the battery disconnect unit no longer functioning properly. In an extreme case, for example in the case of a short circuit, the battery cells could explode.
In order to ensure the safety and function of a battery system, for example a lithium-ion battery system, it is therefore necessary to prevent the formation of condensation water, or to remove the formed condensation water from the battery system.